diff --git a/test/unit_tests/image_stitcher_test.py b/test/unit_tests/image_stitcher_test.py
index f363d8d..01f8b41 100644
--- a/test/unit_tests/image_stitcher_test.py
+++ b/test/unit_tests/image_stitcher_test.py
@@ -8,7 +8,7 @@ import fpdf
 import numpy as np
 import pytest
 from PIL import Image
-from funcy import merge, second, compose, rpartial, juxt
+from funcy import merge, second, compose, rpartial, juxt, rest, first
 
 from image_prediction.estimator.preprocessor.utils import image_to_normalized_tensor
 from image_prediction.image_extractor.extractor import ImageMetadataPair
@@ -127,8 +127,8 @@ class Stitcher:
 
 
 def merge_group(group):
-    def f(pairs):
-        current_pair = pairs.pop(0)
+
+    def merge_with(current_pair, pairs):
 
         to_remove = []
 
@@ -142,7 +142,7 @@ def merge_group(group):
     pairs = list(group)
 
     while True:
-        new_pairs = f(deepcopy(pairs))
+        new_pairs = merge_with(*juxt(first, rest)(pairs))
         if len(new_pairs) == len(pairs):
             break
         pairs = new_pairs